Question

The average length is 4 characters for the strings. I was thinking a binary search might be the fastest starting at position 4. Also I think an inlined templatized function might perform well. This is done in a very tight loop so performance is critical.

The data looks like:

"1234    "
"ABC     "
"A1235   "
"A1235kgo"

Answer 1

char* found = std::find(arr, arr+9, ' ');

Note that ‘no match’ is signaled wuth the end iterator:

bool match = (arr+9) != found;

Note, that

• binary search doesn’t apply unless you characters are in some known ordering.
• std::find is inlined, templatized and will perform to the max if you turn on optimization (e.g. -O3 -march=native for g++)

Edit since you have shown more code, I now realize you actually want to detect (sub)string length. You could use

• std::string::find_first_of
• std::string::find_last_of
• std::string::find
• std::string::rfind
  etc.

Of course, that assumes you’d want to convert the char[] to std::string for the purpose. In practice, that might be a perfectly valid idea, because of SSO (Small String Optimization) found in nearly all implementations of the C++ standard library.
(see Items 13-16 in Herb Sutter’s More Exceptional C++, or Scott Meyers’ discussion of commercial std::string implementations in Effective STL).